1. Field of the Invention
The present invention relates to a multiplex transmission apparatus which comprises a plurality of nodes connected to communication lines for transmission and reception of various kinds of control information in a multiplexed fashion, to/from the communication lines.
2. Description of the Related Art
Recent development of electrical components for vehicles and electronic control of such components has brought an enormous increase in wiring, connectors and control devices arranged in a vehicle body, making a wire harness attached to the vehicle body larger in size and heavier in weight. The increased size and weight of the wire harness limits attaching space in the vehicle body, and degraded flexibility of the wire harness lowers attaching efficiency. Furthermore, the increased weight of the wire harness is directly related to increased weight of the vehicle body.
For the purpose of decreasing the number of wires, connectors and control devices, Japanese Patent Application Laid-Open No. 63-148739 proposes a multiplex transmission system for vehicles which comprises a common communication line for multiplex transmission of plural kinds of control information to operate various electrical components, connectors and control devices in vehicles. The common communication line is connected to a plurality of nodes which perform transfer and reception of control information to/from the line, and various electrical components are appropriately connected to the nodes.
In this multiplex transmission system, the communication line for transmission of multiplexed control information comprises a signal transmission path formed with a wire harness arranged in a vehicle body. The plurality of nodes connected to the communication line are respectively combined with actuators including motors arranged at each node and signal generating devices such as sensors and switches. The respective nodes receive selected control information from the communication line and generate a control signal based on the received control information. The nodes supply the control signal to the actuator to perform an operation control, or generate control information based on a signal from the signal generating device and transmit the information to the communication line. The multiplexed control information transmitted through the communication line is expressed by, e.g., a pulse code modulation (PCM) signal in the form of non-return-to-zero (NRZ) modulated carrier wave signal.
In the abovementioned multiplex transmission system, upon forming a control signal based on control information from the communication line, or upon forming control information based on a signal from the signal generating device, the actuator and the signal generating device usually require operation process by an operation control unit comprising, e.g., a microcomputer, in accordance with control information from the communication line or the signal from the signal generating device. The respective nodes include a transceiver connected to the communication line, an operation control unit connected to the transceiver, comprising e.g., a microcomputer and an input-output processor connected to the operation control unit and either of the actuator or the signal generating device.
The actuators and the signal generating devices which require operation process in the nodes are normally arranged in a vehicle body in a decentralized manner. In the conventional multiplex transmission system, an actuator or a signal generating device which requires operation process is included in almost all the nodes. For this reason, the nodes necessarily include both an operation control unit and an input-output processor. However, the system comprising nodes of this type possesses a problem in lowering cost efficiency.